The invention relates to a method and apparatus for bending thin-walled pipes, in particular pressure gauge springs.
Pressure-gauge springs must be produced of very thin-walled pipe material so that they can sufficiently deform under the interior pressure to be measured. In general, such pressure gauge springs must be bent in an arc of approximately 270.degree..
It is known to use a mandrel bending apparatus in which the pipe to be bent is removed from the end of the mandrel and is simultaneously bent in such a manner that the pipe moves with the rotating forming member. This principle seems to be sound, as it allows to manufacture successively a number of pipe parts from a single elongated pipe piece in a substantially automatic cycle and to subsequently separate each manufactured pipe arc.
Nevertheless, such a mandrel bending apparatus cannot be used when the manufacture of thin-walled pipe material is concerned. Pipes having a wall thickness under 0.2 mm cannot be produced in such a manner because of occurring cracks and/or flexures.
Therefore, it is necessary to manufacture the extremely thin-walled pipe individually and manually in order to render their use appropriate for pressure gauge springs. In this manner, a flexible mandrel is inserted into the pipe which usually has a flat cross section and is then bent manually around the forming member. Thereafter the mandrel is removed from the bent pipe. It is obvious that this bending method is extremely cumbersome and requires a considerable time.